This application is related to Japanese Patent Application No. 2000-306543 filed on Dec. 5, 2000, whose priority is claimed under 35 USC xc2xa7119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a method of preparing a barrier rib master pattern for barrier rib transfer and a method of forming barrier ribs. More particularly, the invention relates to a barrier rib master pattern preparation method and a barrier rib formation method, which are employed for formation of barrier ribs of a display panel such as a plasma display panel (PDP).
2. Description of the Related Art
In recent years, production processes have been established for display panels such as PDPs, particularly, for surface discharge PDPs, allowing for production of large-screen PDPs. Even with the establishment of the production processes, the PDPs still have lower luminous efficiencies, requiring enhancement of the efficiency. PDPs of an ALiS (alternate lighting of surfaces) structure have been developed, which are capable of displaying a high vision image source on an interlace basis to achieve higher performance. However, such PDPs require improvement in driving margin, because display electrodes are arranged with uniform gaps defined therebetween for retention discharge.
Among these PDPs, display panels of an AC-driven tri-electrode surface discharge type are currently dominant. In the display panels, a plurality of address (signal) electrodes are arranged parallel to each other as extending vertically on one of opposed substrates (typically a rear substrate) with barrier ribs interposed therebetween, and pairs of display electrodes for surface discharge are arranged parallel to each other as extending laterally on the other substrate (typically a front substrate) with discharge gaps defined between the respective pairs of display electrodes.
The PDPs of the surface discharge type having the elongated barrier ribs and the linear display electrodes typically have a pixel size of about lmm on a 42-inch wide VGA screen. Where an HDTV-class resolution is required with this structure, the pixel size should be reduced to 500 xcexcm, making the PDP production difficult. For this reason, the PDPs of the ALiS structure have been developed which realize the HDTV-class resolution on a 42-inch interlaced screen.
In the ALiS PDPs, the display electrodes are arranged at regular intervals (generally equidistantly) to define the discharge gaps therebetween. In this case, vertical coupling of discharge spaces in each row is suppressed by spatial barriers and potential barriers. However, a sufficient driving margin cannot be ensured with the spatial barriers, because the discharge gaps are defined between the respective display electrodes. One approach to this problem is to physically suppress the vertical coupling of the discharge spaces by providing barrier ribs of cross grid configuration.
While the aforesaid electrode arrangement has been developed, a variety of barrier rib formation methods have been developed. Exemplary methods hitherto known for the barrier rib formation include a sandblast method suitable for mass-production, a method employing a photosensitive barrier rib material, and a transfer method.
In the sandblast method, a particulate abrasive is blasted onto a dry barrier rib material film with the intervention of a mask pattern to physically cutting unnecessary portions of the film. In this method, the barrier rib configuration can be varied depending on the strength of the film, the particle diameter and shape of the abrasive, and the blasting period.
The method employing the photosensitive barrier rib material includes the steps of projecting a light beam having an exposure wavelength (typically ultraviolet light) onto a photosensitive barrier rib material film of a negative type (photo-curable type) with the intervention of a mask pattern, and removing unnecessary portions of the film by development thereof. In this method, the barrier rib configuration can be varied depending on the sensitivity of the photosensitive material.
The transfer method includes the steps of preparing a master pattern having the same configuration as barrier ribs to be formed, impressing the master pattern in a silicone rubber or the like to prepare an intaglio pattern as a matrix for the barrier ribs, filling the intaglio pattern with a barrier rib material for formation of a barrier rib pattern, transferring the barrier rib pattern onto a glass substrate for formation of the barrier ribs. In this method, the barrier rib configuration can be varied depending on the configuration of the master pattern.
In the AC-driven tri-electrode surface discharge PDPs and the ALiS PDPs described above, cells (discharge spaces) as minimum luminous units are laterally defined between barrier ribs, and a fluorescent layer is formed in each of the cells. Light from the fluorescent layer is reflected on the barrier ribs, so that the luminous efficiency varies depending on the configuration of the barrier ribs, particularly, the taper angle of side walls (side faces) of the barrier ribs. More specifically, the light cannot efficiently be directed toward a display surface depending on the taper angle of the barrier ribs, whereby the light may be repeatedly reflected on the interior of the cell to be partially leaked to the rear side. In the case of the cross grid barrier ribs, flickering dependent on a vertical view angle may occur due to a shadowing effect of lateral barrier ribs, if the lateral barrier ribs have an improper taper angle. Where the barrier ribs are formed by the transfer method, it is necessary to properly taper the barrier rib pattern for easy release thereof.
In the AC-driven tri-electrode surface discharge PDPs and the ALiS PDPs, the luminous efficiency is significantly influenced by the barrier rib configuration, particularly, by the taper angle of the barrier ribs. Further, where the barrier ribs are formed by the transfer method, the release of the barrier rib pattern is significantly influenced by the taper angle of the barrier ribs.
Among the aforesaid barrier rib formation methods, the sandblast method has a difficulty in finely controlling the taper angle of the barrier ribs by controlling the strength of the film, the shape and particle diameter of the abrasive, and the blasting period.
In the case of the method employing the photosensitive barrier rib material, the barrier ribs may have an inversely tapered configuration (having a smaller width at the bottom than at the top) due to attenuation of the light intensity, if they are formed through a single light exposure process. Although the barrier ribs can be formed as having a given cross section by performing the light exposure process several times or by controlling the photosensitivity of the photosensitive barrier rib material, it is difficult to variably control the taper angle of the barrier ribs. Particularly, where the photosensitive barrier rib material contains a filler which blocks light of a specific wavelength, the sensitivity of the photosensitive material is influenced by the filler, making it difficult to control the taper angle.
The transfer method allows for the formation of the straight barrier ribs, but has a lot of problems associated with the formation of the cross grid barrier ribs. Particularly, the preparation of the master pattern in the transfer method is achieved by forming a metal pattern through a mechanical cutting process. This method is applicable only to the preparation of a master pattern for the straight barrier ribs, but it is difficult to prepare a master pattern for barrier ribs of a honeycomb or cross grid configuration.
As described above, the conventional barrier rib formation methods have a difficulty in forming the barrier ribs with a finely controllable taper angle, particularly, in forming the cross grid barrier ribs. This makes it difficult to produce a PDP having a barrier rib configuration which is capable of efficiently directing the light toward a display surface and suppressing the flickering occurring due to a luminous variation.
In view of the foregoing, the present invention is directed to a method of preparing a barrier rib master pattern for barrier rib transfer, which ensures highly accurate and stable formation of a rib pattern having properly tapered side walls by projecting exposure light obliquely onto a photosensitive material with the intervention of a photomask, and to a barrier rib formation method for forming barrier ribs having properly tapered side walls directly on a PDP substrate for production of a PDP which is capable of efficiently directing light toward a display surface and suppressing the flickering.
In accordance with the present invention, there is provided a method of preparing a barrier rib master pattern for barrier rib transfer, comprising the steps of: forming a photosensitive material layer on a substrate; performing oblique exposure by projecting exposure light onto the photosensitive material layer with the intervention of a photomask obliquely with respect to the substrate; and developing the photosensitive material layer; whereby a rib pattern having tapered side walls is formed on the substrate.
In the present invention, the exposure light is projected obliquely onto the photosensitive material layer with the intervention of the photomask for the formation of the rib pattern having the tapered side walls on the substrate. Therefore, the barrier rib master pattern can easily be prepared as having a rib pattern tapered at a desired taper angle to ensure easy release of a barrier rib pattern at the transfer thereof.
Further, the barrier rib master pattern can easily be prepared as having a cross grid rib pattern.
Therefore, barrier rib transfer and release processes can stably be performed with a high yield in the barrier rib formation by the transfer method by employing an intaglio pattern prepared with the use of the barrier rib master pattern.
In a PDP which has barrier ribs formed as having tapered side walls by employing the barrier rib master pattern, light can efficiently be directed toward a display surface. Further, the flickering which may otherwise occur due to shadowing by lateral barrier ribs of the cross grid barrier ribs can be suppressed by the tapered side walls of the barrier ribs.